1. Field of the Invention
The invention relates to a screw extrusion press for processing thermoplastic and not reticulating polymers the conveying screw of which comprises a conveying zone and a mixing zone with at least one mixing ring that extends from the bottom of the screw to the wall of the cylinder and is provided with at least two passage holes.
2. Description of the Related Art
A screw extrusion press of this type is known from DE 2 023 910. There, passage holes extend alternately from the bottom of the screw diagonally to a region near the cylinder and vice versa. In spite of this great construction expense, the homogenization of the molten mass is not satisfactory, this being in particular due to the shape of the passage holes leading from the region near the cylinder to the bottom of the screw. The molten mass is thereby conveyed from a region having a high circumferential speed to a region with a very low circumferential speed at the bottom of the screw, this conflicting with good mixing and homogenization.
The document DE 100 00 938 A1 shows a rotor in a housing with a ring package consisting of mixing rings and partition rings. The mixing rings have grooves on the inflow side, each of said grooves running toward an axially extending channel in the perimeter region of the mixing rings. The partition rings also have longitudinal grooves on their circumference. The mixing grooves and the longitudinal grooves are each limited by the wall of the housing. Transport of the molten plastic occurs through the diverse grooves and bores.
The DE 38 43 576 A1 shows a conveying screw in an extruder. On the conveying screw, there are ring-shaped mixing elements comprising multiple bores leading at an angle to the longitudinal axis of the extruder from the inflow side to the outflow side of the rings. The molten granulate is mixed and in parts conveyed through these bores.